Transmitter



1935- c. w. HANSELL 1,985,924

TRANSMITTER Filed Jan. 31, 1930 2 Sheets-Sheet 2 l l l l l l l l Q a v Q "3 '5 t M Q W i J I INVENTOR v CLARENCE W. HANSELL ATTORNEY Patented Jan. 1, 1935 i UNITED STATES;

1,985,924 TRANSMITTER Glarence W. Hansell, Port Jeffersom lv. T signor to Radio Corporation of America, a"

corporation of Delaware Application January 31, 1930, Serial No. 424,761

8 Claims. (01. 250-17) This invention relates totransmitting appara-' tus and more particularly to transmitting apparatus in which oscillations at carrier frequency are amplified, modulated'in accordance with the wave form of the low frequency signalto be transmitted, and then supplied to an antenna system from which they are radiated.

The general methods of modulation knownheretofore are first, grid modulation, that is, modlO ulation' of the carrier frequency energy by impressing oscillations at signal frequency on the usually necessary to use Smore tubes of a given size? in the final stage of the modulation ire quency amplifier than in the radio frequency amplifier. This necessitates the use, of a number of tubes and consequently increases the amount of apparatus necessary to energize thetubes. This initself'is an undesirable feature in all cases and more so where the transmitter isto be usedior aircraft work. In aircraftwork one of the main requirements is apparatus ofsmall'bulk and light weight.

Briefly and broadly the primary object of :this

invention is to provide a transmitter whichincludes an oscillation generator, a novel amplifier and a novel and efficient meansjof modulating.

the carrier frequency'in the amplifier in accordance with the signal frequency;

such a; device in which the radio frequency out- A further-objectof my invention is to' provide 1 a thermionic generator which dispenses with many of the heretofore necessary choke coils and transformers used in the modulator circuits. v

Another object of my invention is to provide devices of the above nature which-will'maintain The last mentioned method while in general use at the present time has various-disadvantages. One of these isthe large amount of power capacity" necessary in the modulator tubes to obtain modulation by this method. For good" quality it is H putcurrentofthe amplifier tube is asnearly as a frequency constant "enough for most purposes,

but which may'be'readily adapted't'ofus'e with a master oscillator or a'crystal control or both."-

Another object of this invention is to provide a transmitter of the nature designated above 'in' '5: which a single thermionic tube of the screen grid or four element'typ'e serves as an oscillation generator; an amplifier,'and a modulator. The mod ulation frequency is impressedon the carrier wavc generated and amplified by means oI'a' thermionic 10 tube having its anode circiiitassociated-with the screen grid of the four elementf oscillator tube. Thus two tubes are all that-are required in a transmitter constructed in accordance with my invention; j Y

- An added 'object of this invention is to provide I a thermionic generator which requires but-a single thermionic tube of the four-electrode type to produce; modulate; and'amplify'the oscillations} necessaryin aircraftwork. U

A further objectbf my invention is to provide an oscillating'amplifier of the above described type in which the anode circuit is of a nature to] obtainfthe highamplificatio n possible from a screen"grid tube. Y

lhave found hat by modulating through the screen grid of athermionic tube of the "screen grid type, as set forth'in detail hereinafter, con-' siderably less modulating fpowerfcapacity is re quired and only one source of anode voltage is required. Modulating the carrier frequency in'this manner therefore reduces; the number of tubes necessary and; requires a 'single source of anode voltage. This"consquentlyreduces the "apps-5 ratus necessary. ;This inturn reduces the total: 35: weight of; the transmitter, which is fOf extreme importance where;'; as pointed out above, the transmitter is ;to beused on aircraftE Y Brieflytheabove objects are attainedin accordance wit one form of thepresent invention g g l by theuse ofa'noveltransmittbr which asingle i Another'object' of my invention is to provide screen grid tubejserves the purpose of an oscillator, an amplifier'and a 1 nodu1ator tube. The modulation frequencies may be impressed on the screen grid of this tube 'through'a resistance coupled amplifier stage the input circuit of which is-con'riectedto a source of modulation energy; v This oscillator may be used as described above; or if conditions require, may be controlled'as to frequency by a master oscillator-or a piezo-eleotric crystal; q 3 i As will be obvious a considerable reduction in weight of apparatus isobtained'by the use of a transmitter' constructedas above since nomodu' lation choke coils with their heavy cores are neeessary, a single tube operates as an oscillator amplifier and modulator and a single small tube fed by a telephone transmitter furnishes the modulating frequencies.

In the ordinary plate modulated radio telephone circuit the anode losses in the oscillator tube are highest when the losses in the modue lator tubes are lowest and they vare lowest when the modulator tube losses are highest. Therefore, by combining the two functions in a single tube we obtain more uniform anode losses in the tube throughout a cycle of modulation and do not increase the maximum losses very much above the value which would be reached if the tube were used as an oscillator .or modulator alone.

In another form of my invention the use of the modulation frequency amplifier is done away with by connecting a high voltage microphone directly between the control grid and cathode of the four electrode tube which serves the purpose of oscillation generator, amplifier and modulator. In this form of the-invention the frequency of the oscillation generator is controlled by means of the selected-one of a plurality of calibrated piezo crystals. In this modification anode potential is supplied by-"means -of an air-driven dynamotor while filament heating current is supplied by means of the battery used toenergize thelighting circuits of'the plane.

In 'thisimodification, by means of a novel switching arrangement, two frequencies can be used; one of which is used for calling and the other ;of which ,is usedfor working the station called. This is practical where the calling and working frequencies are not too widely separated. For, convenience of operation a start-stop switch, a wave-change switch, a --send-receive switch, a microphone landan antenna meter are located within easy access of the person or persons operating the transmitter. In actual practice I propose to locate the send-receive switch on the-microphone and the other switches and the meter -in-some convenient place in the cock- ;pit so that the radio apparatus as well as the plane may be operated by the pilot. In each'of the above modifications the oscillations are fed from a tank circuit connected to the anode of the screen grid oscillating amplifier 'into the antennasystem from which they .are'radiated.

A more complete understanding ofmy invention and its-advantages will-be hadfrom the .following detailed description thereof andfrom said description when readin connection with the,

drawings through whichl-ike reference numerals indicate like parts; and in which,

a single four-electrode oscillation generator, modulated through a single three electrode ltube;

Figure2 isa typical characteristic Kcurves'howing the relation between the amplitude .of the radio frequency output of theoscillator used the apparatus shown in Figural plotted against the voltage applied to thegr-id of the tube applying the modulation frequency to the oscillator; and, r

Figure -3 showsa novelarrangement which uses but a single tube.

Referring to the drawings and -in particular -.to.

Figure -1 thereof 1 indicates .a four-electrode tube which generates in a well known manneroscilla through biasing resistance 12 between the grid 13 and cathode 3 of thermionic tube 1. To insure sustained oscillation of tube 1 a coupling condenser 14 is connectedbetween grid 13 and one end of inductance 4 as shown in Figure 1.

' Modulating frequencies are provided by means of a microphone 15 connected in series with biasing resistance 16 between the control electrode 17 and cathode 18 of modulation frequency amplifier '19. 'The modulation frequency repeated and amplified in thermionic tube 19 and appearing on the anode 20 thereof is impressed on the screen grid electrode 21 of thermionic tube 1 through a resistance 22-. To prevent oscillations at radio frequencies appearing-on the screen grid 21 of thermionic tube 1 from being introduced into modulation amplifier 19 a by-pass condenser 23 is connected between screengrid 21 and the cathode circuit of thermionic tube 1. current in thermionic tube 19 is obtained from high voltage winding 6 of dynamotor through a charging resistance 24. Heating current for the filaments of thermionic tubes 1 and 19 is provided directly from the-direct current source 25 when the switch 26 is-closed. Source 25 also provides current for operating the dynamotor 27. To lower the voltage applied to the filament of tube 19 which may require less voltage than tube 1 and to protect the filament of tube 19 a resistance 29 is shunted across the filament terminals of tube 19. For further protection of the entire low voltage circuit a fuse 30 is connected in series with one side of filament heating current circuit. Radio frequency currents are shunted around the high :voltage winding 6 of dynamotorf27 by .means of a by-pass condenser 31 in parallel with said winding.

In operation when the switch 26 is closed the windings of dynamotor 2'7 are energized thereby setting the dynamotor in operation. Simultaneously the filaments of tubes '1 and 19 are energized and high, potential voltage is supplied to the anodes of tubes 1 and '19 from the high voltage winding 6 while resistance 16 and 12 insure that the proper biasing potentials are applied to w the control grid electrodes of land 19. Due to Figure 1 shows anovel transmitter which usesthe'jcoupling between the anode and cathode circuits of oscillation generator 1 oscillations are produced at a frequencydetermined by tank circuit-,4, 5. ,These oscillations are modulated in accordance with voice frequencies impressed by meansof microphone 15 on the input elements of amplifier 19. The carrier frequency modulated-in accordance with said voice frequencies is set up in antenna circuits 8, 7, G from whic it is radiated.

-By the use of a standard :tube of low impedance sufficient modulation for practical :purposes may be obtained. This will be seen :from Figure 2; which is a curve showing the relation between the amplitude of radio frequencyoutput, that is, the amplitude of the oscillations in the antenna circuit with reference to the negative voltage applied by means :of the potential :drop across resistance 16.150 theicontrol electrode of .19.

Anode space ulatedinflsaid tube. "In this modification-the al- 1 In Figure:- 3 is-shown :an arrangement whereby;

ofthe screen grid-andcontrol grid of the four:

electrode tubeg-"ias will be more fully pointed out' hereinafternf'w 1 1 '1 '.-'Referring in'particular ito Fig.3, 40 isa thermionic tube: which not only generates'thecarrier frequency but also is associated .with means whereby the carrier frequency generated is mod-.

ternating current plate circuit includes a tank circuit comprising ,an inductance .41 tuned .-by a variable capacity 42.? Anode potential is provided by connecting the mid. tap of inductance 41 through-the high voltage. winding: 43 of dynamotor 43 and resistance'44 to' the negative termi-j nal of theifilament 45. Potential is'applied to the.

grid electrode" 48 by connecting said electrode to the high voltage Twinding 43 through a. charging resistance 46;- Radio frequencies are-prevented from entering the winding43 by inserting a radio frequency choke 47 in said last namedconnection. Oscillationsin the. alternating current anode circuit ortank circuitareinsured by a .cir- 'cuit including one orthe other of a pair "of piezo electric crystals 49, arranged to connect the free end of winding 41'to the gridielectrode 48. The frequency of said. oscillations is determined by one or; the other of said pair of crystals 49 and 50 arranged through contacts 51and 52 and armature 53 to be connected in series between, the last named grid andthe freeendof inductance 41. 'I'he dielectric capacity of each crystalf should balance'the-capacity of the tube to prevent undesired oscillations or parasitics to be set tential 'toelectr'o'de 55. Any radio frequency cur-' rents appearing this circuit are shunted around the high voltage windingibymeans of a bi-pass condenser 71% Current for heating the filament of thermi onictube 40 is obtained from the-lighting bat tery 5 4 when the switch -56 is closed thereby. completing the circuit from the batterygthrough the filament to ground; The voltage applied across resist saidfilament is regulatedby avariable ance 57." I

When the switch -56isclosed, current from the battery also fl ows from battery '54throughj switch? 56, conductor 58 and audio f requencyi choke coil 59 tofthe motor of dynamotor 43 en'e1 gizing w'inding 60 of dynamotor 43thereby put ting the dynamotor in operation-and generating the high voltage direct current in -winding 42 whichis-appliedtothe anode and control electrodes of 40. Radio frequency disturbances are eliminated from the high voltage winding of the generator, the high voltage winding ofthe microphone and from the battery 54 by means of condensers '70, 71 and '72 respectively while condenser 73 and choke coil 59 prevents modulation from the commutator of the dynamotor 43 returning to the battery and the vacuum tube circuits. An antenna circuit comprising an antenna is coupled by means of winding 81 in series therewith to the inductance 41 of the tank circuit. A thermo-couple 82 is provided so that the antenna current may be observed by means ofan'ammeter connected in shunt to said:

thermo-couple. The desired crystal for control-. ling the frequency'of the oscillation generator is;putzin circuit :automaticallywhen contact 90.

is. closed and manuallyfloperated switch 91 is 1 moved intorone of its. closed positions; thereby including onehalf of the solenoid winding 92 in series with-battery 54.*-;This energizes winding 92 and operates the armature '53 associated therewith in one direction or the other closing contactfil or 52: thereby putting either crystal 4901'. 50 in series between the space charge'grid 48 of 40 and oneend of theinductance 41.,the

other end ofwhich is connected to the plate 39.

In "operation switch56 is closed. -This energizes the filament. .of oscillation generator 40:

consequently armature 93 remains in theopenv position breaking the. grid circuit. However, when is closed and 91 is moved into position to insert the desired fcrystalin. series withithe grid circuit of the oscillation generator 40 oscillations are generated ataa'frequency determined byythe crystal put in circuit. These oscillations after being modulated in accordance with modulation, frequencies impressed by the high voltage microphone '54 on the grid .55 of tube40 are.

impressed by means of the tank circuit 41-, 46 on the :aerial 80through inductance 31. The moduej lated oscillations are radiated from 80. vInactual operation crystals,49 and 50 maybe selected so i that oneisused' for the calling frequency while theotheris used for the signalling frequency. As pointedout above this is practical-where said frequencies are not widely separated.

In actual operation it may be sometimesdesired toxstop signallingfor a short time as for,

instance long enough to receive a ;-signal, that is, to stop the generator from generating oscillations without disconnecting the dynamotor from; the'batteries. This-is desirable since it is pref-- erable,that-the'heatingcircuits for 40 are not allowed *0001 during receiving .of signals. By

meansofthe send-receive switch 90'the'osci11ation circuits may be interrupted without interrupting the energizing circuits for 40..

Although forpurposes of-illustration I have shown the at present preferred form of my invention and set forth the operation thereof, I

do not wish to limit'myself thereby except as marked out-,inqthe claims appendedheret'o.

.Iclaim: v

1. Radio, apparatus including. a thermionic oscillationagenerator including a four electrode tube of the screen grid type, meansassociated with the controlgfid of said tube and with the anode o'fzsaid tube for generatingoscillations at carrier ,frequencys-meansincluding a resistance lating said carrier frequency oscillation in accordance with the signal to be transmitted, a load circuit and means for impressing the modulated oscillations on said aerial circuit.

5. and-asource of signal frequency connected with the screen grid' electrode of said tubevfor moduw 2. In a radio transmitter an oscillation gener-, i

ator including a thermionic tube having an anode,

a cathode, and a plurality of auxiliary electrodes, means including a circuit connected between one of said auxiliary electrodes and the cathode of said tube and coupled to a circuit connected besaid circuits for determining thefrequency of said oscillations, means f or modulating said ihighrfre quency oscillations with signals through a high resistance connected to the other' auxiliary electrode of said tube, :an antenna circuit coupled to said :anodecathode circuit, and means-for apply-' ing high potential to the anode :cathode circuit of said tube and energizing the auxiliary electrode thereofincluding aihigh voltage winding of r I trode.

a dynamotor. I c

3. Radio'frequency oscillation generating appara'tus including a thermionic tube having'ian anode, a cathode',rand a pluralityof auxiliary elec trodes, means including a circuit connected 'between one of said auxiliary electrodes and the cathode of said tube and coupled to a circuit connected between the anode of said thermionic tube and the cathode thereof for-generatingaoscillations at high frequency, a piezo electric: crystal associated with said oscillation'circuit to: determine the frequency thereof, said crystal having a capacity sufficient to balance the capacity between the electrodes in said tube, means associated with another of said auxiliary electrodes for modulating said high frequency, and a load circuit associated with said anode cathode circuit.

4. Radio apparatus including a thermionic high frequency oscillation generator having an anode, cathode and auxiliary electrodes, a circuit connected between the anode and cathode of said thermionic tube, a circuit connected between one of the said auxiliary electrodes and said cathode,f

means for tuning-said circuits-to the desired "frequency, means for coupling said last'named circult 'to said anode cathode circuit, a plurality-of frequency determining means associated with said auxiliary electrode cathode circuit, means for modulating the high frequencies generated in said circuits including apparatus responsive to'modulating frequenciesconnected through a resistance between the other auxiliary electrode of. said thermionic tube and its cathode, a dynamotorrhaving a high voltage winding connected between the anode cathode of said thermionic tube, a source. of cathodepotential, includinga battery having one terminal connected to the cathode through :a switch and the other terminal grounded, means for stopping oscillations in said circuits without=.

de-energizing the electrodes thereof, aridia relay for controlling the frequency determining means.

5. Means for producing high frequency oscillations and for impressing signal modulations on said oscillations comprising, a thermionic'tube in" cluding an evacuated closure member, an anode,"a cathode and apair of auxiliary electrodes therein,

an oscillation circuit connected between said-- anode and cathode, a circuit connected between one of said auxiliary electrodes and said' cathode, a source of potential, a dynamotoi' energized by said source, a circuitconnecting said-sourceiof potential to said cathode to energize the same, a-

high voltage winding on said dynamotor, said highivoltage winding :being connected with said first .two named circuits 'to :applyenergiz'ing potentials to the"electrodessinxsaid circuits, said circuits-being coupled-together 'to produce :sus-

tained os'cillations .insaid tube and said circuits, and means for modulating the oscillations produced by signal potentials including a source of signal "potentials and a resistance in series between the E'cathode and the other auxiliary elec- T .6. Means for "producing high frequency oscillations of constant frequency comprising, athermionic' tube having an anode, a cathode and a plurality of auxiliary electrodes, an inductance connectedibetween the anode and cathode of said tube, a source of potential said'connection, a pluralitywofpiezo-electr'ic"crystals, a switching device having aimovable contact connected with an auxiliary-electrode'insaid tube and a pluralityoffixed contacts, each'connected withone of the electrodes of one'of said crystals, a connection between the other'electrode :of the other of said crystals andrsaid inductance, and a circuit for applying: direct current potentials from said source tosaid auxiliary electrode connected with the 'movable member 'of "said switch, whereby when saidswitchis-in contact with one of said fixed :contactsbscilla'tions are produced in said circuitgthe frequency of which oscillations is deter-minedin part by the piezo-electric crystal connected'lo'y'said'switch between said auxiliary electrode and said inductance;

'FZJA" signalling system comprising an oscilla tion generator as recited 'm-claim 6, and means for modulating the oscillationsigenerated thereby including, :a source of modulating potentials,-

and a resistance connected between'the cathode and'the other auxiliary-electrode of said tube.

:8. Signalling means including; a thermionic tube "havingan anode, a'cathode, and a plurality of grid electrodes, an oscillation circuit connected ance'connecting the anode-of said last named tube to-the other auxiliary electrode in said first named tube,,;:, andjiaflqresistive connection between the anodeof-said last named tube and said source :of direct-current potential.

CLARENCE, -W. HANSELL. 

